Terraform is an open-source Infrastructure as Code (IaC) tool developed by HashiCorp that allows you to define and provision infrastructure using declarative configuration files. Unlike imperative tools that require you to specify step-by-step instructions, Terraform uses a declarative approach where you describe the desired end state.

Key differences from other IaC tools:

• Provider-agnostic: Works with multiple cloud providers (AWS, Azure, GCP, etc.)
• State management: Maintains a state file to track real-world resources
• Plan and apply workflow: Shows changes before applying them
• Immutable infrastructure: Replaces resources rather than modifying them in place

The Terraform workflow consists of four main steps:

1. Write: Create configuration files (.tf) defining your infrastructure
2. Initialize: Run terraform init to download providers and modules
3. Plan: Run terraform plan to preview changes before applying
4. Apply: Run terraform apply to create/modify/destroy infrastructure

terraform init
terraform plan
terraform apply
terraform destroy  # when cleanup is needed

Providers are plugins that enable Terraform to interact with cloud platforms, SaaS providers, and APIs. They define resource types and data sources available for use.

Example AWS provider configuration:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

provider "aws" {
  region = "us-west-2"
}

Resources are infrastructure components that Terraform creates, manages, and destroys. They represent the desired state of infrastructure.

Data sources allow Terraform to fetch information about existing infrastructure or external systems without managing them.

# Resource - creates new EC2 instance
resource "aws_instance" "web" {
  ami           = "ami-12345678"
  instance_type = "t2.micro"
}

# Data source - fetches existing VPC info
data "aws_vpc" "default" {
  default = true
}